4. Investigate the hydrolysis of halogenoalkanes

Controls: Volume and concentration of ethanol, silver nitrate solution and the halogenoalkanes, water bath temperature

Errors

Mixing up test tubes – keep them labelled

Measuring cylinder

Exact point of precipitation – subjective

Results

Time for part 1: 1-chlorobutane > 1-bromobutane > 1-iodobutane

Time for part 2: 1-bromobutane > 2-bromobutane > 2-bromo-2-methylpropane

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5. Investigate the oxidation of ethanol

Method

1. Place a few anti-bumping granules in a 50cm3 pear shaped flask

2. Add 10cm3 acidified sodium dichromate to the flask

3. Set up the flask for reflux

4. Mix 2cm3 ethanol with 5cm3 water

5. Place the flask in a beaker of iced water and add the ethanol solution dropwise down the condenser into the flask (this must be done slowly)

6. When all the ethanol has been added, heat the flask gently with a small Bunsen flame so the solution boils for 10mins

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5. Investigate the oxidation of ethanol

7. Perform the following tests:

a. Measure the pH of the distillate using universal indicator paper

b. Add a few drops of acidified potassium dichromate solution to 1cm3 of the distillate and warm the mixture in a 60°C water bath

c. Add a quarter of a spatula of calcium carbonate powder to 1cm3 of the distillate.

d. Add a 1cm long length of magnesium ribbon to 1cm3 of the distillate

e. Add 1cm3 of Fehling's solution to 1cm3 of the distillate and warm the mixture gently using a water bath

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5. Investigate the oxidation of ethanol

Results

Oxidation of ethanol to ethanoic acid

a. Low pH so acid

b. No change (no oxidation or reduction)

c. effervescence as CO2released

d. effervescence as H2released (acid)

e. No change as fully oxidised already

CH3CH2OH + 2[O] → CH3COOH + H2O

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6. Chlorination of 2-methylpropan-2-ol

Method

1. Pour 20cm3 2-methylpropan-2-ol and 70cm3 conc. HCl into a large conical flask with a bung

2. Swirl the contents of the flask, then remove the bung to release the pressure before replacing it and continuing to swirl

3. Continue this process for around 20 minutes when there should be 2 layers in the flask, the upper one being the crude product

4. Add approx. 6g of powdered anhydrous CaCO3 to the flask and swirl until dissolved (to ensure that any unreacted alcohol is in the lower aqueous layer

5. Transfer the reaction mixture into a separating funnel and allow the mixture to settle before running off and discarding the lower layer (retaining the upper layer in the funnel)

6. Add approx. 20cm3 of sodium hydrogencarbonate solution, swirl, and remove the bung at frequent intervals to release the CO2 produced before discarding the lower aq layer

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6. Chlorination of 2-methylpropan-2-ol

7. Repeat the washing with sodium hydrogencarbonate, shake the separating funnel and release the CO2 at frequent intervals

8. Run off and discard the lower layer, ensuring none remains in the tap

9. Run off all the organic layer into a small conical flask and add a spatula full of anhydrous sodium sulfate

10. Add a bung and swirl the contents to mix and then occasionally until the liquid looks completely clear

11. Decant the organic liquid into a 50cm3 pear-shaped flask

12. Set the flask up for distillation

13. Collect the fraction boiling between 50˚C and 52˚C and place the pure product into a labelled sample tube

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6. Chlorination of 2-methylpropan-2-ol

Results

Test the distillate by placing a few drops in a test tube. Add 5cm3ethanol and 1cm3NaOH(aq)and warm in a water bath. Add excess nitric acid followed by a few drops of silver nitrate solution. A white precipitate will form indicating the presence of chloride ions.

(CH3)2CHOH + HCl → (CH3)2CHCl + H2O

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7. Identify unknown organic (l) and inorganic (s)

Method: Part 1 – for organic liquids A, B, C

Start each test by placing 10 drops of each liquid into 3 separate test tubes

1. Add a 1cm depth of bromine water to each test tube and shake

2. Add acidified potassium dichromate to each test tube and warm in a 60˚C water bath for 5 minutes

3. Add 1cm3 of Fehling’s solution to each test tube and heat the resultant in a water bath

10. Construct EC cells and measure E

Control: Same salt bridge (same solution and type of filter paper), same voltmeter and wires

Errors

Not using standard conditions of 100KPa, 1moldm-3, 298K

Impurities may still remain on the metal strips

Results

Record electrode potentials for each cell

Calculate Ecell­

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11. Amount of Fe in Fe tablet using titration

Method

1. Crush the iron tablets using the pestle and mortar

2. Transfer the crushed tablets to a weighing boat and measure their combined mass

3. Empty the crushed tablets into a small beaker and reweigh the weighing boat

4. Add 100cm3 1.5moldm-3 sulfuric acid into the beaker and stir to dissolve as much as possible

5. Filter the solution into a volumetric flask and add washings (with sulfuric acid). Make up to the mark with distilled water, stopper and shake

6. Pipette 25cm3 of this solution into a conical flask

7. Titrate the iron(II) solution with potassium manganate(VII) solution until the mixture has just turned pink (on standing the pink colour will disappear due to a secondary reaction between the KMnO4 and another ingredient in the tablet)

8. Repeat the titration until concordant results are obtained

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11. Amount of Fe in Fe tablet using titration

Variables

Independent: Volume of iron(II) solution

Dependent: Volume of potassium manganate(VII) solution

Controls: Concentrations, temperature

Errors

Human error in judging the end point – colour change is subjective so use a white tile

Burette, pipette, mass balance, volumetric flask – can be measured

Burette – bring down to eye level and read the bottom of the meniscus

Results

Form equation

Calculate: average titre, moles MnO4-, moles Fe, mass of Fe in each tablet, percentage of Fe in each tablet

13.a) Rate of the I -C H reaction using titration

2. Start the stop clock as soon as you add 50cm3 0.02moldm-3 iodine solution, and shake the beaker to mix well

3. Withdraw 10cm3 of the mixture and transfer it to a conical flask

4. Stop the reaction in this sample by adding a spatula of sodium hydrogencarbonate, noting the exact time this happens

5. Titrate the sample with 0.01moldm-3 sodium thiosulfate(VI), until there is a pale yellow colour, then add a few drops of starch indicator (blue) before continuing to titrate until the solution turns colourless

14. Determine the Ea for Br and Br

Colour change is subjective – use a white tile and have the same person judge it each time

Pipette, thermometer uncertainty can be measured

Results

Convert temperatures to kelvin, calculate 1/temp., and take natural logs of the times

Plot ln(t) (y axis) against 1/T (x axis)

Calculate the activation energy using the Arrhenius equation and the gradient of the graph

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15. Analyse organic and inorganic unknowns

Method: Inorganic ions

1. Flame test

2. Use sodium hydroxide to identify metal cations

3. Use silver nitrate to identify halide ions

4. Test for sulfate ions

5. Test for carbonate ions

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15. Analyse organic and inorganic unknowns

Errors

Mixing up the unknown compounds – label well

Colours are subjective

Measurement uncertainty

Results

Compound A formed a blue-green flame and turned the lime water cloudy, suggesting that it is copper carbonate

Compound B formed an orange flame and a white precipitate with BaCl, suggesting that it is sodium sulfate

Compound C formed a brick red (or orange-red) flame, a white precipitate with NaOH and a cream/yellow precipitate with AgNO3which dissolved in concentrated ammonia, suggesting that it is calcium bromide

Compound D formed a green precipitate with NaOH, and a white precipitate with AgNO3, suggesting that it is iron(II) chloride

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15. Analyse organic and inorganic unknowns

Method: Organic analysis

1. Test for alkenes

2. Test for aldehydes

3. Test for carboxylic acids

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15. Analyse organic and inorganic unknowns

Errors

Mixing up the unknown compounds – label well

Colours are subjective

Smells are subjective

Measurement uncertainty

Results

Solution X decolourised the bromine water, suggesting that it is an alkene

Solution Y formed a silver mirror, suggesting that it is an aldehyde

Solution Z formed a fruity smell suggesting that it is a carboxylic acid

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16. Synthesise aspirin from 2-hydroxybenzoic acid

Method

1. Weigh 2g 2-hydroxybenzoic acid and place in pear-shaped flask clamped and suspended in a beaker of water